FractalSnow machichara (from http://www.davidflanagan.com/2010/12/let-it-snow.html)
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/* |
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* The snowflake() function below is the cool part of this hack. |
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* It draws a fractal, but includes only a single line-drawing command. |
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* A 4th order Koch snowflake consists of 768 connected line segments, |
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* and this function draws them all with c.lineTo(0,len). The secret |
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* is the way it manipulates the transformation matrix before drawing |
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* each line. Probably not the most efficient way to write the code |
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* but a fun exercise in <canvas> transformations. |
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* |
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* The code to make the snowflakes fall is pretty standard CSS animation. |
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* Not the cleanest code I've written, but I need to get back to finishing |
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* the 6th edition of JavaScript: The Definitive Guide. |
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*
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* This ought to work in IE9 beta, since that browser supports <canvas>. |
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* But it doesn't seem to. I took the shortcut of using window.innerHeight |
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* and window.pageYOffset, and I'm guess that is what is breaking it. |
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*
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* Copyright 2010 by David Flanagan |
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* http://creativecommons.org/licenses/by-nc-sa/3.0/
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*/ |
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(function() { |
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// If we don't have a working <canvas> element, apologize and quit
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if (!document.createElement("canvas").getContext) { |
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alert("Your browser doesn't support <canvas>\n" + |
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"No snow for you!\n" + |
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"Please try a recent version of Firefox, Chrome or Safari"); |
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return; |
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} |
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// Draw a level-n Koch Snowflake fractal in the context c,
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// with lower-left corner at (x,y) and side length len.
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function snowflake(c, n, x, y, len) { |
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c.save(); // Save current transformation
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c.translate(x,y); // Translate to starting point
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c.moveTo(0,0); // Begin a new subpath there
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leg(n); // Draw the first leg of the fractal
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c.rotate(-120*deg); // Rotate 120 degrees anticlockwise
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leg(n); // Draw the second leg
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c.rotate(-120*deg); // Rotate again.
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leg(n); // Draw the final leg
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c.closePath(); // Close the subpath
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c.restore(); // Restore original transformation
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// Draw a single leg of a level-n Koch snowflake.
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// This function leaves the current point at the end of
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// the leg it has drawn and translates the coordinate
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// system so the current point is (0,0). This means you
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// can easily call rotate() after drawing a leg.
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function leg(n) { |
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c.save(); // Save current transform
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if (n == 0) { // Non-recursive case:
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c.lineTo(len, 0); // Just a horizontal line
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} |
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else { // Recursive case: _ _
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// draw 4 sub-legs like: \/
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c.scale(1/3,1/3); // Sub-legs are 1/3rd size
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leg(n-1); // Draw the first sub-leg
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c.rotate(60*deg); // Turn 60 degrees clockwise
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leg(n-1); // Draw the second sub-leg
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c.rotate(-120*deg); // Rotate 120 degrees back
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leg(n-1); // Third sub-leg
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c.rotate(60*deg); // Back to original heading
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leg(n-1); // Final sub-leg
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} |
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c.restore(); // Restore the transform
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c.translate(len, 0); // Translate to end of leg
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} |
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} |
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var deg = Math.PI/180; // For converting degrees to radians
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var sqrt3_2 = Math.sqrt(3)/2; // Height of an equilateral triangle
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var flakes = []; // Things that are dropping
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var cover = new Image(); |
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cover.src = "http://covers.oreilly.com/images/0636920016045/cat.gif"; |
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var coverwidth = 180, coverheight = 296; |
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var scrollspeed = 80; // How often we animate things
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var snowspeed = 500; // How often we add a new snowflake
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var rand = function(n) { return Math.floor(n*Math.random()); } |
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// Add a new snowflake at the top of the viewport
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function createSnowflake() { |
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var order = 2 + rand(3); // 2nd, 3rd, or 4th order fractal
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var size = 10 + rand(90);
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var x = rand(window.innerWidth - size); |
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var y = window.pageYOffset; |
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// Create a <canvas> element
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var canvas = document.createElement("canvas"); |
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canvas.width = size; |
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canvas.height = size*sqrt3_2*4/3; |
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canvas.style.position = "absolute"; |
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canvas.style.left = x + "px"; |
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canvas.style.top = y + "px"; |
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canvas.style.zIndex = 100 + rand(100); |
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// Draw a translucent snowflake into the transparent canvas
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var c = canvas.getContext("2d"); |
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c.strokeStyle = "rgba(0,0,0,0.5)"; |
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c.fillStyle = "rgba(255,255,255,0.75)"; |
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snowflake(c,order,0,Math.floor(sqrt3_2*size),size); |
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c.fill(); |
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c.stroke(); |
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// Add the canvas to the document and to our array of snowflakes
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document.body.appendChild(canvas); |
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flakes.push({elt:canvas, x: x, y:y, vy:3+rand(3)}); |
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// Once in a while, add something different to the mix
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if (rand(100) == 1) { |
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// drop the cover image
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var img = document.createElement("img"); |
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img.src = cover.src; |
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var scale = Math.random()/2 + .25; |
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img.width = Math.round(coverwidth * scale); |
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img.height = Math.round(coverheight*scale); |
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img.style.position = "absolute"; |
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var x = rand(window.innerWidth - img.width - 150); |
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var y = window.pageYOffset; |
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img.style.top = y + "px"; |
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img.style.left = x + "px"; |
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img.style.zIndex = 200; |
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document.body.appendChild(img); |
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flakes.push({elt:img, x:x, y:y, vy:4}); |
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// and drop a message, too
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var div = document.createElement("div"); |
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div.style.width = "120px"; |
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div.style.height = "40px"; |
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div.style.position = "absolute"; |
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x = x + img.width + 20; |
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y = y + 30; |
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div.style.top = y + "px"; |
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div.style.left = x + "px"; |
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div.style.zIndex = 200; |
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document.body.appendChild(div); |
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div.innerHTML = "<a style='color:#fff' href='http://oreilly.com/catalog/0636920016045/'>Save 40% with code AUTHD</a>"; |
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div.style.border = "solid red 2px"; |
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div.style.backgroundColor = "#c00"; |
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div.style.border = "solid black 1px"; |
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div.style.font = "bold 10pt sans-serif"; |
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div.style.color = "#fff"; |
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div.style.textAlign = "center"; |
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div.style.padding = "3px"; |
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flakes.push({elt:div, x:x, y:y, vy:4}); |
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} |
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} |
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// This function animates the flakes falling down the screen
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function moveSnowflakes() { |
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var maxy = window.pageYOffset + window.innerHeight; |
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var i = 0; |
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while(i < flakes.length) { // Loop through the array of flakes
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var flake = flakes[i]; |
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flake.y += flake.vy; |
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if (flake.y > maxy) { |
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// The flake has scrolled off, so get rid of it
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document.body.removeChild(flake.elt); |
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flakes.splice(i, 1); |
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continue; |
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} |
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flake.elt.style.top = flake.y + "px"; // Move the flake down
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// Move the flake side to side
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if (flake.vx == undefined) flake.vx = 0; |
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flake.x += flake.vx; |
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flake.elt.style.left = flake.x + "px"; |
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// Sometimes change the sideways velocity
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if (rand(4) == 1) flake.vx += (rand(11) - 5)/10; |
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if (flake.vx > 2) flake.vx = 2; |
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if (flake.vx < -2) flake.vx = -2; |
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i++; |
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} |
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} |
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function snow() { |
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// Start creating snowflakes and moving them down the screen
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var scrolltimer = setInterval(moveSnowflakes, scrollspeed); |
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var snowtimer = setInterval(createSnowflake, snowspeed); |
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//
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var controls = document.createElement("div"); |
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controls.style.position = "fixed"; |
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controls.style.left = "2%"; |
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controls.style.top = "5px"; |
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controls.style.width = "96%"; |
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controls.style.padding = "5px"; |
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controls.style.zIndex = 1000; |
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controls.style.backgroundColor = "#c00"; |
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controls.style.border = "solid black 1px"; |
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controls.style.borderRadius = "4px"; |
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controls.style.font = "bold 10pt sans-serif"; |
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controls.style.color = "#fff"; |
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document.body.appendChild(controls); |
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controls.innerHTML = |
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"Koch snowflake fractals from " +
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"<i><a style='font:inherit; color:#fff' " + |
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"href='http://oreilly.com/catalog/0636920016045/'>" + |
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"Canvas Pocket Reference</a></i>. " + |
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"<a style='font:inherit; color:#fff' " + |
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"href='http://www.davidflanagan.com/2010/12/let-it-snow.html'>" + |
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"Learn how it works</a>. Happy Holidays! "; |
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var stopbutton = document.createElement("button"); |
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stopbutton.innerHTML = "Stop"; |
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controls.appendChild(stopbutton); |
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stopbutton.onclick = function() { |
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clearInterval(scrolltimer); |
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clearInterval(snowtimer); |
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for(var i = 0; i < flakes.length; i++) |
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document.body.removeChild(flakes[i].elt); |
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document.body.removeChild(controls); |
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}; |
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} |
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if (document.readyState === "complete") snow(); |
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else window.addEventListener("load", snow, false); |
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}()); |
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